diff --git a/test/input.c b/test/input.c
index 5813e6dc9..9b5db8991 100644
--- a/test/input.c
+++ b/test/input.c
@@ -1390,8 +1390,8 @@ dix_valuator_alloc(void)
         assert(v->numAxes == num_axes);
 #if !defined(__i386__) && !defined(__m68k__) && !defined(__sh__)
         /* must be double-aligned on 64 bit */
-        assert(((void *) v->axisVal - (void *) v) % sizeof(double) == 0);
-        assert(((void *) v->axes - (void *) v) % sizeof(double) == 0);
+        assert(offsetof(struct _ValuatorClassRec, axisVal) % sizeof(double) == 0);
+        assert(offsetof(struct _ValuatorClassRec, axes) % sizeof(double) == 0);
 #endif
         num_axes++;
     }